feat(confidence-engine): constrain reconstruction chat output

lib/llm/provider.js

@@ -1,3 +1,6 @@
+import { z } from "zod";
+import { reconstructionV2Schema } from "../reconstruction/schema.js";
+
 /**
  * Provider abstraction — the app calls getProvider() which returns an object
  * with a generateReconstruction(scenario, modelName) method.
@@ -59,6 +62,7 @@ function recoverJson(raw) {
 }
 
 let _chatSupported = null;
+const reconstructionJsonSchema = z.toJSONSchema(reconstructionV2Schema);
 
 async function detectChatSupport(baseUrl, modelName) {
   if (_chatSupported !== null) return _chatSupported;
@@ -113,7 +117,7 @@ class OllamaLlmProvider {
     } catch { /* failed silently — defaults to false */ }
 
     // ================================================================
-    // Step 2: Try /api/chat if supported and format:json works
+    // Step 2: Try /api/chat if supported with the reconstruction schema
     // ================================================================
     if (chatSupported) {
       try {
@@ -128,7 +132,7 @@ class OllamaLlmProvider {
             model: modelName,
             messages: [{ role: "user", content: prompt }],
             stream: false,
-            format: "json",
+            format: reconstructionJsonSchema,
           }),
           signal: controller.signal,
         });